There is known a blood glucose level measuring device (blood component measuring device) for measuring a blood glucose level. The blood glucose level measuring device quantifies a blood glucose level by optically measuring (calorimetrically measuring) a color that is developed by a test strip depending on the amount of glucose in blood.
The conventional blood glucose level measuring device includes a photometric unit having a light-emitting element and a light-detecting element. The photometric unit measures the color of the test strip by applying light to the test strip and measuring the intensity of reflected light.
The photometric unit has a passage for passing therethrough the light to be applied to the test strip and the reflected light from the test strip. The passage is open in a portion of the photometric unit which faces the test strip.
The photometric unit of the above component measuring device suffers a problem in that dust or foreign matter tends to be trapped in the photometric unit. The problem has heretofore been addressed by Japanese Patent Laid-Open No. Hei 3-95438 and Japanese Patent Laid-Open No. Hei 3-95439.
Japanese Patent Laid-Open No. Hei 3-95431 and Japanese Patent Laid-Open No. Hei 3-95440 have proposed placing a transparent plate on the front surface of a photometric unit to prevent dust from entering the component measuring device.
With the conventional blood glucose level measuring device, however, since the opening is not sealed in a liquid-tight manner, blood applied to the test strip may be trapped into the passage in the photometric unit, and it is difficult to remove the trapped blood from the test strip.
Furthermore, if a liquid such as water and an aqueous solution of ethanol is used to wash away a stain such as dust, blood, urine, and fingerprint, then the liquid may possibly enter the blood glucose level measuring device.
If foreign matter such as water and blood is introduced into the passage in the photometric unit, then the measured value of the blood glucose level varies, resulting in a reduction in the measurement accuracy.
Stains such as dust, dirt, fingerprint and blood may be applied to the transparent plate. The applied stains are liable to cause the measured value of the blood glucose level to vary, resulting in a reduction in the measurement accuracy. Therefore, stains on the transparent plate need to be detected.
Heretofore, it has been customary to detect such stains according to a white level checking process. According to the white level checking process, a white pattern is placed at the tip end of the photometric unit, and when a stain is applied to the transparent plate, the sum of the amount of reflected light from the white pattern and the amount of reflected light from the transparent plate is reduced.
More specifically, a stain is detected by the white level checking process as follows: A tip having a test strip (white) is mounted on the photometric unit. The tip is irradiated with light emitted from the light-emitting element of the photometric unit, and reflected light reflected from the tip is detected by the light-detecting element. A stain on the transparent plate is detected based on the amount of light detected by the light-detecting element. If the amount of light detected by the light-detecting element is smaller than a predetermined threshold, then it is determined that the transparent plate is stained.
According to the white level checking process for detecting a stain, however, the strong reflected light from the test strip and the weak reflected light from the stain on the transparent plate are mixed with each other, tending to fail to detect a stain on the transparent plate highly accurately.